Duct with vanes having selectively variable pitch

ABSTRACT

A gas turbine has a plurality of variable pitch inlet guide vanes. Each inlet guide vane has a vane lever arm for varying the pitch of the vanes in response to arcuate movement of the vane lever arms. Sector actuation segments interconnect adjacent vane lever arms so that circumferential movement of a sector actuation segment causes arcuate movement of the interconnected vane lever arms. Actuation means cooperates with the sector actuation segments and an actuation ring to selectively move the sector actuation segments circumferentially with respect to the actuation ring. The vanes, then, can be varied in pitch in unison or in individual sectors.

United States Patent [1 1 Wanger Jan. 21, 1975 DUCT WITH VANES HAVINGSELECTIVELY VARIABLE PITCH [75] Inventor: Robert P. Wanger, Fairfield,Ohio [73] Assignee: General Electric Company,

Cincinnati, Ohio [22] Filed: Feb. 27, 1974 [21] Appl. No.: 446,231

FOREIGN PATENTS OR APPLICATIONS 608,292 11/1960 Canada 415/162 878,98810/1961 Great Britain ..4lS/l62 Primary Examiner-Henry F. RaduazoAttorney, Agent, or FirmDerek P. Lawrence; Lee H. Sachs [57] ABSTRACT Agas turbine has a plurality of variable pitch inlet guide vanes. Eachinlet guide vane has a vane lever arm for varying the pitch of the vanesin response to arcuate movement of the vane lever arms. Sector actuationsegments interconnect adjacent vane lever arms so that circumferentialmovement of a sector actuation segment causes arcuate movement of theinterconnected vane lever arms. Actuation means cooperates with thesector actuation segments and an actuation ring to selectively move thesector actuation segments circumferentially with respect to theactuation ring. The vanes, then, can be varied in pitch in unison or inindividual sectors.

9 Claims, 3' Drawing Figures DUCT WITH VANES HAVING SELECTIVELY VARIABLEPITCH BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to a duct and more particularly to such a duct havingvariable pitch vanes therein.

2. Description of the Prior Art In conventional gas turbines, axial flowfans and compressors are used to compress the air entering the gasturbine. Such gas turbines include an inlet which diffuses the incomingair in order to more efficiently utilize the ram effect of the highvelocity air moving into the gas turbine. Such diffusion increases theoverall pressure ratio of the gas turbine as measured between ambientair pressure and the pressure of the air exiting the downstream end ofthe compressor.

In order to most efficiently utilize the fan and compressor, the airflow entering the upstream end of each must have a precise axialorientation which orientation is determined by the pitch of the bladescomprising the respective first rotor stages. In order to provide thisprecise axial orientation of the incoming air, inlet guide vanes havebeen used in the prior art. Inlet guide vanes are a series of stationaryvanes, spaced circumferentially around an annular duct immediatelyupstream of the associated rotor (fan or compressor) inlet, which vaneshave a precise pitch with respect to the incoming air flow.

It is known in the prior art that the air flow through the inlet willapproach the inlet guide vanes at varying angles of attack depending onmany factors of gas turbine operation. In order to overcome the problemof varying angle of attack at different operating conditions, inletguide vanes whose pitch may be varied have been used.

However, it has been found that, under some circumstances, distortion inthe form of axial velocity variations at the upstream end of the inletresult in circumferential variation of the angle of attack of the airflow at or near the inlet to the respective rotor stage. It is clearthat the use of inlet guide vanes whose pitch is varied, but all ofwhich have the same pitch at any given time, cannot compensate for thiscircumferential variation in angle of attack.

The present invention solves this problem through the provision of aduct having vanes in which the pitch of individual groups of vanes,comprising two or three vanes each, can be selectively or uniformlycontrolled. In order to facilitate the description of this invention,the references which follow pertain only to compressors and theapplication of this invention thereto, but the concepts are equallyapplicable to fans.

SUMMARY OF THE INVENTION It is therefore a primary object of thisinvention to provide an arrangement for selectively varying the pitch ofa portion of a plurality of vanes disposed in a duct, while maintainingthe capability of varying the pitch of all such vanes in unison.

In accordance with the present invention, a duct has an annular flowpassage defined interiorly thereof and comprises an actuation ring whichis mounted for circumferential movement relative to the duct. Aplurality of variable pitch vanes are disposed in the annular flowpassage and each vane includes a vane lever arm which is moved arcuatelyto vary the pitch of the vanes. A plurality of sector actuation segmentsare provided, each such segment being mounted to predetermined numbersof adjacent vane lever arms so that the vane lever arms are movedarcuately as the sector actuation segments are moved circumferentially.A plurality of actuation means, which actuation means correspond innumber to the number of sector actuation segments. are provided. Theactuation means cooperate with the actuating ring and correspondingsegments to move the corresponding segment circumferentially relative tothe actuation ring. In addition, the actuation means serve to link thesegments to the actuation ring so that all the vanes may be varied inpitch in unison by circumferential movement of the actuation ring alone.

DETAILED DESCRIPTION OF THE DRAWINGS A more complete understanding ofthe invention may be had by reference to the specification when taken inconjunction with the accompanying drawings, wherein:

FIG. 1 represents a gas turbine jet engine incorporating the presentinvention;

FIG. 2 illustrates a portion of one embodiment of the present inventionshowing a first actuation mode; and

FIG. 3 is a view similar to FIG. 2 and illustrates a second actuationmode.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1, a gasturbine 10 is depicted which includes a compressor 12, a combustorsection 14, a turbine 18 and exhaust nozzle 20 in a conventional manner.(As indicated above, the concepts hereof are applicable also to fans inturbofan engines, but for simplicity the present turbojet illustrationwill suffice.) A duct 21 at the upstream end of compressor 12incorporates a circumferentially extending set of inlet guide vanes 22disposed in annular flow passage defined interiorly of duct 21.

Referring now to FIGS. 2 and 3, each inlet guide vane 22 is mounted inthe flow passage of the duct 21 for rotation about its axis 24 so thatits pitch may be varied. Each vane 22 includes a vane lever arm 26 forvarying the pitch of vane 22 in response to arcuate movement ofcorresponding lever arm 26.

A plurality of sector actuation segments 28 is provided. Each segment 28interconnects adjacent predetermined numbers, here shown as three (3),of vane lever arms 26. Circumferential movement of a sector actuationsegment 28 (as shown by arrow 30) causes arcuate movement of the vanelever arms 26 interconnected therewith and thus varies the pitch ofvanes 22. Since a conventional number of vanes 22 is eighteen (18),(only six (6) of which are shown for simplicity), in the application ofthe present invention to the gas turbine of FIG. 1, there will be atotal of six (6) sector actuation segments 28 (only two (2) of which areshown for simplicity). Each sector actuation segment 28 cooperates witha segment lever arm 32. Segment lever arm 32 is shown as extension ofone of vane lever arms 26, but those skilled in the art will recognizethat a separate lever arm may be secured to the sector actuationsegments without departing from the spirit of the invention.

An actuation ring 34 extends circumferentially around duct 21. Duct 21is circumscribed by the actuation ring when the present invention isused as shown in the presently embodied gas turbine application, but

those skilled in the art will recognize that the actuation ring 34 mayextend only partially around the duct 21 without departing from thespirit of the invention. Actuation ring 34 is mounted forcircumferential movement relative to duct 21 by a plurality of actuationring arms 36 which are pivoted to duct 21 and to actuation ring 34.Suitable means, such as hydraulic actuators 35 are provided for movingactuation ring 34 circumferentially relative to duct 21.

A plurality of sector actuation means is provided corresponding innumber to the number of segments 28 which are provided, here indicatedto be six (6). The sector actuation means move sector actuation segments28 circumferentially relative to actuation ring 34. Each sectoractuation means includes a linear hydraulic actuator 42 having acylinder 44 and piston 46 movable in cylinder 44. Cylinder 44 ispivotably mounted to actuation ring 34 by pivot 48 and piston 46 has apiston rod 47 which is pivotably mounted to its corresponding segment 28at sector lever arm 32 by pivot 50.

In operation, with gas turbine 10 mounted to an aircraft for propellingthe aircraft, certain flight modes of the aircraft will producedistortion in the form of circumferential variations in the axialvelocity of the air entering the inlet. These axial velocity variationsaround the circumference of the inlet are transformed into angle ofattack variations when they reach the upstream end of compressor 12where inlet guide vanes 22 are located. Since the angle of attack of theair flow reaching the first stage of the compressor 12 can varycircumferentially within annular flow passage 23, it is desired to beable to selectively vary the pitch of inlet guide vanes 22 to correctthese circumferential variations of angle of attack. Sector actuationsegments 28 and actuation ring 34 may be advantageously positionedcircumferentially in order to vary the pitch of inlet guide vanes 22 ingroups of three and thus to compensate for these circumferentialvariations in angle of attack and thereby increase the efficiency of gasturbine 10, as shown in FIG. 3.

In certain other modes of operation, the engine inlet is not subjectedto distortion, but there is advantage in changing the angle of attack ofthe incoming air with respect to all of the rotor blades in the firstrotor stage. In this situation, actuator 35 will be employed to rotateactuation ring 34, but the individual sector actuation means maintainedin fixed position. As a result, the motion of ring 34 will be carriedequally by lever arms 32 to the sector actuation segments 28.Consequently, all of the stator vanes 22 will be changed in pitch by anequal amount determined by the motion of ring 34. (FIG. 2).

Thus, the present invention offers a uniquely effective means forsolving the distortion problem, while maintaining the capability ofvarying the angle of attack of the air flow as a whole.

Although the present invention has been described in connection withducts used to introduce air flow to the compressor of a gas turbine, itwill be clear to those skilled in the art that it is not intended to berestricted to such an application. For example, there may beapplications where the relation of sector actuation segments 28 and vanelever arms 26 are more advantageous than that shown herein. Inaccordance with the requirements of such an application, those skilledin the art will recognize that greater or less selectivity may beobtained by having fewer or more, respectively, vane lever arms 26interconnected by a single sector actuation segment 28 or that a singlesector actuation segment may be interconnected with other thancontiguous vane lever arms without departing from the spirit of theinvention.

Similar modifications, other than that one specifically pointed out, canbe made without departing from the invention, and it is intended bytheappended claims to cover all such modifications as fall within thetrue spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

l. A duct of the type having an annular flow passage defined interiorlythereof, the duct comprising:

a. an actuation ring mounted for circumferential movement relative tosaid duct;

b. a plurality of variable pitch vanes disposed in said annular flowpassage wherein each said vane includes a vane lever arm for varying thepitch of said vane in response to arcuate movement of said vane leverarm;

c. a plurality of sector actuation segments wherein each said segment ispivotably mounted to predetermined numbers of said vane lever arms formoving said vane lever arms arcuately in response to circumferentialmovement of said sector actuation segment; and

d. a plurality of actuation means corresponding in number to saidplurality of sector actuation segments wherein each said actuation meanscooperates with said actuation ring and said corresponding sectoractuation segment for moving said corresponding sector actuation segmentcircumferentially relative to said actuation ring whereby the pitch ofsaid vanes may be selectively varied.

2. The duct recited in claim 1 wherein each said sector actuationsegment includes a segment lever arm for moving said segmentcircumferentially in response to arcuate movement of said segment leverarm.

3. The duct recited in claim 2 wherein each said actuation meanscomprises a linear hydraulic actuator having a cylinder and a pistonmovable in said cylinder.

4. The duct recited in claim-3 wherein said cylinder is pivotablymounted to said actuation ring and said piston is pivotably mounted tosaid corresponding segment lever arm.

5. The duct recited in claim 1 wherein said vane lever arms comprisingeach said predetermined number are contiguous.

6. The duct recited in claim 5 wherein said plurality of vanes is 18 innumber, equally spaced with respect to the circumference of said duct,said plurality of sector actuation segments is six in number, and eachsaid predetermined number of vane lever arms is three.

7. The duct recited in claim 1 wherein said actuation ring circumscribessaid duct.

8. The duct recited in claim 7 further comprising a plurality ofactuation ring arms for mounting said actuation ring to said duct.

9. The duct recited in claim 1 in combination with a gas turbine of thetype having a compressor and inlet guide vanes for directing flow to thecompressor, wherein said variable pitch vanes comprise said inlet guidevanes.

1. A duct of the type having an annular flow passage defined interiorlythereof, the duct comprisIng: a. an actuation ring mounted forcircumferential movement relative to said duct; b. a plurality ofvariable pitch vanes disposed in said annular flow passage wherein eachsaid vane includes a vane lever arm for varying the pitch of said vanein response to arcuate movement of said vane lever arm; c. a pluralityof sector actuation segments wherein each said segment is pivotablymounted to predetermined numbers of said vane lever arms for moving saidvane lever arms arcuately in response to circumferential movement ofsaid sector actuation segment; and d. a plurality of actuation meanscorresponding in number to said plurality of sector actuation segmentswherein each said actuation means cooperates with said actuation ringand said corresponding sector actuation segment for moving saidcorresponding sector actuation segment circumferentially relative tosaid actuation ring whereby the pitch of said vanes may be selectivelyvaried.
 2. The duct recited in claim 1 wherein each said sectoractuation segment includes a segment lever arm for moving said segmentcircumferentially in response to arcuate movement of said segment leverarm.
 3. The duct recited in claim 2 wherein each said actuation meanscomprises a linear hydraulic actuator having a cylinder and a pistonmovable in said cylinder.
 4. The duct recited in claim 3 wherein saidcylinder is pivotably mounted to said actuation ring and said piston ispivotably mounted to said corresponding segment lever arm.
 5. The ductrecited in claim 1 wherein said vane lever arms comprising each saidpredetermined number are contiguous.
 6. The duct recited in claim 5wherein said plurality of vanes is 18 in number, equally spaced withrespect to the circumference of said duct, said plurality of sectoractuation segments is six in number, and each said predetermined numberof vane lever arms is three.
 7. The duct recited in claim 1 wherein saidactuation ring circumscribes said duct.
 8. The duct recited in claim 7further comprising a plurality of actuation ring arms for mounting saidactuation ring to said duct.
 9. The duct recited in claim 1 incombination with a gas turbine of the type having a compressor and inletguide vanes for directing flow to the compressor, wherein said variablepitch vanes comprise said inlet guide vanes.